Can one convert a car with the standard power locks, "hit the unlock button on the remote to unlock the doors" to a keyless entry system where the doors would unlock automatically when you're in proximity to the car? I think like the 2012 Volt has? I tried googling, but the billion hits that come up all seem to be the standard "keyless" entry where you have to physically press an unlock button on the remote which is not what I am looking for.
I'm not asking about modifying a Volt. This would be for an entirely other car with power locks, hence the post in off-topic.